1. Field of the Invention
The present invention relates to a control system for a fuel cell. More specifically, the present invention relates to a control system for a fuel cell which controls a fuel supply to a fuel cell and an output from the fuel cell which may be provided with a reforming device.
2. Description of Related Art
A conventional solid polymer membrane type fuel cell includes a cell in which a solid polymer electrolyte membrane is sandwiched by an anode and a cathode, and a stack is formed by a plurality of laminated cells (hereinafter referred to as a fuel cell). In general, hydrogen is supplied to the anode as a fuel and air is supplied to the cathode as an oxidizing agent so that hydrogen ions generated at the anode by a catalytic reaction pass through the solid polymer electrolyte membrane and move to the cathode to electrochemically react with oxygen to generate power.
A fuel cell unit provided with a reforming device is disclosed, which utilizes an alcohol type compound, such as methanol, or a hydrocarbon type compound, such as gasoline, as a raw material and produces a hydrogen-enriched fuel by modifying such raw materials, for instance, in the Japanese Unexamined Patent Application, First Publication No. 6-76846.
In such a fuel cell unit including a reforming device, a discharged fuel from the fuel cell is transferred to a combustion unit in which it is to be burned and the heat generated in the combustion unit is utilized to vaporize raw fuel materials in a vapor generation unit. The fuel vapor produced in the vapor generation unit is supplied to the reforming unit.
However, in the above-mentioned example of the conventional fuel cell unit, there are problems that, for instance, a current required for a fuel cell unit cannot be obtained immediately when a load is being increased and more current is needed. That is, there is a certain time delay (or lag time) between, for instance, the increase of the amount of the raw fuel materials supplied to the vapor generation unit and the time that the output of the fuel cell which corresponds to the required current is generated. Accordingly, the response to the load cannot be appropriately controlled if this time delay is not properly apprehended.
Also, if an excessive amount of the raw fuel materials are supplied to the vapor generation unit exceeding the certain vaporization capacity of the unit when a relatively large current is required to be generated, the raw fuel materials which were not vaporized remains in the vapor generation unit. The remaining raw fuel materials may prevent a stable control of the fuel cell.
The present invention was achieved in consideration of the above problems and its objectives include providing a control system for a fuel cell, which is capable of improving the responsiveness to the load change by appropriately carrying out a fuel supply process and suitably outputting a current generation command.
The present invention provides a control system for a fuel cell, including a vapor generation unit which produces a fuel vapor by vaporizing a liquid fuel; a fuel reforming unit which reforms the fuel vapor so as to produce a hydrogen-enriched reformed fuel; a fuel supply unit which supplies the hydrogen-enriched reformed fuel from the fuel reforming unit to the fuel cell; a combustion unit which burns a discharged fuel discharged from the fuel cell and supplies to the vapor generation unit a quantity of heat generated by burning the discharged fuel; a fuel vapor temperature detection unit which detects the temperature of the fuel vapor; a temperature detection unit which detects the temperature of the combustion unit; a current detection unit which detects the current generated by the fuel cell; and a control unit which calculates quantity of heat retained by the vapor generation unit utilized for vaporizing the liquid fuel based on the temperature of the fuel vapor, the temperature of the combustion unit, and the generated current, the control unit controlling a fuel supply command value for the fuel supply unit and/or a current generation command value for the fuel cell based on the calculated quantity of heat retained by the vapor generation unit.
According to the above control system for a fuel cell, it becomes possible to accurately calculate the fuel supply command value and the current generation command value in accordance with the estimated quantity of heat retained by the vapor generation unit. Accordingly, the output responsiveness and the current generation efficiency of the fuel cell may be improved.
In accordance with another aspect of the invention, the control unit sets a control constant for the fuel supply command value and/or the current generation command value, the control constant including at least one of a lag time, a time constant, and an acceleration rate.
According to the above control system for a fuel cell using the control unit, the output responsiveness and the current generation efficiency of the fuel cell may be further improved by setting the lag time, the time constant, and the acceleration rate.
The present invention also provides a vehicle utilizing a fuel cell as an energy source, including a control system for the fuel cell which includes: a vapor generation unit which produces a fuel vapor by vaporizing a liquid fuel; a fuel reforming unit which reforms the fuel vapor so as to produce a hydrogen-enriched reformed fuel; a fuel supply unit which supplies the hydrogen-enriched reformed fuel from the fuel reforming unit to the fuel cell; a combustion unit which burns a discharged fuel discharged from the fuel cell and supplies to the vapor generation unit a quantity of heat generated by burning the discharged fuel; a fuel vapor temperature detection unit which detects the temperature of the fuel vapor; a temperature detection unit which detects the temperature of the combustion unit; a current detection unit which detects the current generated by the fuel cell; and a control unit which calculates quantity of heat retained by the vapor generation unit utilized for vaporizing the liquid fuel based on the temperature of the fuel vapor, the temperature of the combustion unit, and the generated current, the control unit controlling a fuel supply command value for the fuel supply unit and/or a current generation command value for the fuel cell based on the calculated quantity of heat retained by the vapor generation unit.
In accordance with another aspect of the invention, the control unit provided with the above vehicle sets a control constant for the fuel supply command value and/or the current generation command value, the control constant comprising at least one of a lag time, a time constant, and an acceleration rate.